Organosilicon dendrimer

Krska, S. W. Son, D. Y. Seyferth, D. Organosilicon Dendrimers. In Silicon-Containing Polymers. The Science and Technology of Their Synthesis and Applications-, Jones, R. G., Ando, W., Chojnowski, J., Eds. Kluwer Dordrecht, 2000 pp 615-641. 

Scheme 1. Construction of organosilicon dendrimers using a tetra-directional inicia-tor core.

All the above described reactions proceed cleanly in nearly quantitative yields (80-95%). The new dendrimers display excellent solubility in most organic solvents. The structures of the novel organosilicon dendrimers were confirmed by elemental analysis, infrared spectroscopy, mass spectrometry, and H, C. and Si NMR spectroscopy. 

Figure 1. Sil H) NMR spectra of the organosilicon dendrimers GICl, G2Cl, G1H, and GKallyDj, at 59.3 MHz in CDClj.

This section describes synthetic approaches to the various classes of organosilicon dendrimers. Applications of these materials will also be discussed. In this review, specific dendrimers will be labeled G-X, where is equivalent to the number of layers (or generations, G) around the core, and X represents the endgroups bound to each silicon atom in the outermost layer. This labeling system does not take into account the core or the branching of the dendrhner. Since carbosilane dendrimers are by far the most well-studied of the silicon-based dendrimers, they will be discussed first. 

Cuadrado and co-workers have reported the synthesis of chromium-containing organosilicon dendrimers.334 These dendrimers, 282, have chromium tricarbonyl units incorporated pendent to the terminal aromatic rings.334 Synthesized via the reaction of the silane dendrimer precursor with chromium hexacarbonyl, complete complexation was not possible due to steric hindrance at higher generations. Electrochemical studies showed that the oxidation of the chromium atoms occurred reversibly in the absence of a nucleophilic species and that the chromium tricarbonyl units behaved as isolated redox centers. 

Dvornic, P. R. Owen, M. J., Poly(amidoamine organosilicon) Dendrimers and Their Derivatives of Higher Degree of Structural Complexity. In Synthesis and Properties of Silicones and Silicone-Modified Materials, Clarson, S. J. Fitzgerald, J. J. Owen, M. J. Smith, S. D. Van Dyke, M. E., Eds. American Chemical Society Washington, DC, 2003 Vol. 838, pp 236-259. 

Muzafarov, A. M. Rebrov, E. A., Erom the Discovery of Sodiumoxyorganoalk-oxysilanes to the Organosilicon Dendrimers. J. Polym. Sci., Part A Polym. 

As discussed in Sect. 3, the a-orbitals of silicon overlap with the Jt-system of the chromophore if the silicon is directly attached by a single bonds to the 7t system. Despite this a-Ji-interaction, silicon does not facilitate conjugation between two Ji-systems connected by a siUcon bridge. Therefore silicon does not extend the Ji-system which will have consequences for organosilicon dendrimers, in which ji-conjugated units are connected either by siUcon atoms which build branches in... 

Nakayama and Lin have reported on the first organosilicon dendrimer SisTie, containing 16 2,5-thienylene rings, connected via tetrasubstituted silicon atoms [123]. SisTie was synthesized by the reaction between a tetralithium... 

Nakayama J, Lin JS (1997) An organosilicon dendrimer composed of 16 thiophene tings. Tetrahedron Lett 38 6043-6046... 

Organosilicon dendrimers containing chromium tricarbonyl moieties pendent to peripheral aromatic rings (101) have been synthesized by Cuadrado. These organometallic dendrimers were isolated following reaction of a precursor silane dendrimer with chromiiun hexacarbonyl. It was not possible to effect complexation of every aromatic ring due to steric hindrance. Cyclic voltammetry of these materials indicated that oxidation of the chromium atoms occurred reversibly in the absence of nucleophilic species and that the chromium tricarbonyl imits behaved as isolated redox centers. 

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